Changed no stylesheets to False to retrieve basic styling information from Instapaper. Added CSS to italicize captions/quotations and change the text colour back to black from the default #222 that Instapaper defines in the .size3font class. Added in a line to remove the LABEL tags from the returned HTML so that headers are not duplicated.

So far I've had no problems with any articles and no images are centred and captions/quotes stand out from the rest of the article better. Hopefully this can help out someone else too.

EDIT: I've also submitted this as a proposed enhancement to the bitbucket repo for the plugin just in case.